With a power supply device, a distributed type energy storage device, an electric automobile, or the like that employs a battery, in order to use the battery optimally and effectively, a control device is used that detects the state of the battery and controls charging and discharging of the battery. For the state of the battery, there may be employed its state of charge that represents the what amount the battery is charged or what amount of electric charge that can be discharged remains (hereinafter termed its “SOC”, these being the initial letters of “State Of Charge”), what amount of charge remains, its state of health that represents what extent the battery has deteriorated or has weekend (hereinafter termed its “SOH”, these being the initial letters of “State Of Health”) or the level of deterioration, or the like.
In order to detect the state of the battery, the battery control device performs processing to obtain the SOC and/or the SOH and/or the like on the basis of information that is measured, such as the voltage, the current, the temperature and so on of the battery. Generally the temperature of the battery among the measured information is obtained by measuring the surface temperature via a temperature sensor installed upon the surface of the battery, and is used for the processing for detecting the state of the battery. If it is possible to use the internal temperature of the battery, i.e. the true temperature of its cells, in the processing for detecting the state of the battery, then it is possible to perform detection of the battery state, such as its SOC or SOH, more accurately.
An internal temperature detection device for a battery is known, with which it is arranged to estimate the internal temperature of the battery without fitting any temperature sensor directly to the interior of the battery (for example, refer to Patent Document #1). With this device, the internal temperature of the battery is estimated from the surface temperature of the battery and from the output of a fan that is used for cooling the battery.